I don't know if I've ever seen a book disqualified. Some people have voluntarily withdrawn their nominations, but it seems the club's stance has always been that, besides the six-month rule, the process itself will be what determines what fits in a given month. So without the six-month rule, just three people could ensure that the same book is nominated every month.
Honestly, I think you might like Lolita being nominated every month because it would give you something to complain about.

Not that it's terribly relevant to the discussion but books are sometimes removed due to no e-availability.